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Interesting but not surprising! I have some bicycle components which I bought just to have available in case I ever needed them and it worked out that those same components, as good as they are, then later got discontinued by the manufacturer, but at least I do have them. ISIS seems to be a great system but gotta have bearings to keep ISIS working. and so maybe stocking up on a few extra sets of bearings might be worthwhile.

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Among unicyclists ISIS is a popular system which apparently uses non-standard bearings. Now, I am not talking about going into the bearing business but having a few extra sets of those bearings on hand could not only satisfy one's own future needs but could also become a trading item among fellow unicyclists, especially if those non-standard bearings ever become non-available to the little, tiny unicycling market for which those bearings are intended. Just consider that without good bearings ISIS becomes useless.

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wow, not an unusual size! about $8 american dollars on ebay just do a little looking.

I see that Unicycle.Com does sell ISIS bearings on ebay. About $30 delivered for two. That is about twice the cost of "normal" standard bearings and a little more then getting them directly from UDC. I don't see any other ebay sellers that has them.

It is strange that the bearing manufacturer does not sell them. Maybe they have some kind of restriction or just not profitable to mess with them because of the very low demand.

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Thanks, good to hear! That suggests, not confirms but suggests, that China has some need or use for these bearings and so at least for now it seems safe to assume these bearing are standard bearings. But I would also do just as you have done for that kind of money, that if I needed one set of bearings then I would order five sets, to then have four spare sets, just in case. At UDC the lower grade unis use 40mm OD bearings but the more expensive higher grade unis with ISIS use the 42mm OD bearings such as these, and so for the small money cost of these bearings it seems worthwhile to have a few extra, spare bearing sets at hand.

Bear in mind that not all ball bearings are created equally though. I've bought some 17x42x12 (for my square taper freewheels) and although they work, they're definitely not made to the same quality as the bearings you can buy from UDC.

Maybe someone who has some 42 22 12 unicycle.com bearings can post a pic here of the bearings, with the part numbers shown. That might be useful to find more sources, too.

I also found something called KRIS HOLM KH ISIS MOMENT HUB Bearing Set from RCbearings , available at RCbearings or Amazon that's NOT the correct 42 x22x12 MM bearing size, so stay away from this. I think he said they were 20mm ones.

And I'm sure the pictures aren't the actual bearing in most listings.

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Bear in mind that not all ball bearings are created equally though. I've bought some 17x42x12 (for my square taper freewheels) and although they work, they're definitely not made to the same quality as the bearings you can buy from UDC.

I missed that one, pretty cheap price...
I did learn a whole bunch of stuff on bearings, including the bearing tolerance ratings, ABEC-1, ABEC-3 and ABEC-5 tolerance ratings. So I don't have a lot of hope that I'm getting anything but the lowest quality.